Use of Lithiated Shielding Material
Enriched 6Li-containing materials are utilized in various locations around the NCNR. Common examples include: LiF, Lithoflex, lithiated glass, lithiated poly, and lithiated sintered materials. These materials have become popular for various shielding applications since neutron absorption by 6Li does not result in subsequent gamma emission. However, neutron absorption by 6Li does produce radioactive tritium with a half-life of about 12.3 years. Recent experience has shown that irradiation of 6Li-containing materials can result in the production of tritiated byproducts (other than tritium gas) that can result in spreadable contamination if improperly handled.
The performance advantages of 6Li-containing materials for shielding should be weighed against the handling disadvantages described in this memorandum. Where possible you should consider substituting other neutron absorbing materials, for example, those containing 10B.
- When handling neutron irradiated 6Li-containing materials, the tritiated byproducts can be easily transferred and appropriate handling and contamination control procedures are required.
- You should always wear gloves when directly handling irradiated 6Li-containing materials.
- The neutron irradiation history of 6Li-containing materials is not always known. It should be assumed that all such materials have been in a neutron beam and therefore have the potential for tritium contamination unless explicitly known otherwise.
- The low energy betas from the tritium decay cannot be detected using G-M or NaI survey meters. Health Physics is available to assess for tritium contamination if necessary.
- Items containing 6Li that will be routinely handled should be assembled so that the 6Li-containing portion is encapsulated in another material whenever possible.
- Please contact Health Physics before modifying or disposing of any irradiated 6Li-containing materials.
- Effective contamination control requires proper storage of 6Li-containing materials. Please notify Health Physics of all 6Li-containing materials which are not part of permanent shielding (e.g. not the 6LiF plates in the instrument beam shutter) so that they can assess the storage procedures that are in use.
- Proper storage procedures for this type of radioactive material includes appropriate containers (e.g. plastic bags) and labels.
- For your convenience, a centralized storage area for unused 6Li-containing materials, especially Lithoflex, has been set up in the E-wing basement. Use of this storage area should be coordinated through Health Physics. Currently, most of the unused Lithoflex inventory is stored at this location. Materials that you store there can be bagged separately and labeled with your name if you desire.
Last modified 11-March-2003 by website owner: NCNR (attn: Jeff Krzywon)